The hydrocarboxylation of olefinically unsaturated compounds using rhodium catalysts and iodide promoters in which the reactant is dissolved in a compatible solvent is disclosed in Craddock et al. U.S. Pat. No. 3,579,552.
The hydrocarboxylation of butadiene in methylene chloride using a rhodium catalyst and an iodide promoter is disclosed in U.S. Pat. No. 4,622,423.